1. Field of the Invention
The present invention relates generally to a blind. More particularly, a blind slats lifting device is proposed, wherein a lifting cord is wound about a winding drum which rotates and moves in the longitudinal direction of a head box.
2. Description of the Related Art
Slat lifting devices are well known when used in window blinds. One of the conventional lifting devices is shown in FIG. 12. In this device, an operation cord 42 is hung from an end of a head box 41. A pair of winding drums 43 are provided in the head box. The winding drums 43 can rotate, and can also move in the axial direction thereof. By operating the operation cord 42, lifting cords 44 are wound about the winding drums 43 to lift slats 45.
When the slats 45 remain at their lowest position, the winding drums 43 are placed at positions shown as solid lines in FIG. 12. When the slats 45 are lifted up to the top position, the drums 43 move to positions shown as two-dot chain lines in FIG. 12. The moving stroke of the drums 43 depends on the winding length of the lifting cords and the diameter of the winding drums 43.
In the foregoing slats lifting device, a spacing L1 must be reserved between a wind starting position of the lifting cord 44 and an end of the head box 41. The space must be longer than the stroke of the winding drum 43 in order to prevent the drums 43 from protruding from the ends of the head box 41. Accordingly, the slats 45 also protrude outwardly the same distance from positions where ladder cords 46 support the slats 45. The slats 45 are longer than an interval between the ladder cords 46 by twice the protrusion length L1. It may cause drooping, warping and bending of the slats 45 and uneven alignment at times of angle adjustment. In the foregoing slats lifting device as described above, it is difficult to provide a blind with a minimum length substantially equal to housing lengths of the winding drums 43.